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Small bodies · Space Codex

Main asteroid belt

Leftovers that Jupiter's gravity kept from ever forming a planet.

Rocky debris between Mars and Jupiter

Small bodies
  • Last reviewed 10 Oct 2026
  • 3 sources

At a glance

Main asteroid belt at a glance, with sources
MeasureValueSource
RegionAbout 2.2–3.3 AU from the SunNASA Science: Asteroids (opens in a new tab)NASA Science: Asteroids (opens in a new tab)
Largest memberCeres, 939 km across, about 25% of the belt's massNASA Science: Ceres facts (opens in a new tab)NASA Science: Ceres facts (opens in a new tab)
Second largest4 Vesta, about 525 km, almost 9% of the massNASA Science: 4 Vesta (opens in a new tab)NASA Science: 4 Vesta (opens in a new tab)
Composition classesCarbonaceous (C), stony (S) and metal-rich (M)NASA Science: Asteroids (opens in a new tab)NASA Science: Asteroids (opens in a new tab)
Kirkwood gapsCleared by orbital resonances with JupiterNASA Science: Asteroids (opens in a new tab)NASA Science: Asteroids (opens in a new tab)
SpacingBodies are typically hundreds of thousands of km apartNASA Science: Asteroids (opens in a new tab)NASA Science: Asteroids (opens in a new tab)

Key points

Millions of rocky and metallic bodies, from dust to the dwarf planet Ceres, spread so thinly that spacecraft cross it without danger.

  • Spacecraft cross it without dodging rocks
  • Ceres holds about a quarter of its mass
  • Source of most meteorites that reach Earth

Why no planet formed

Jupiter's gravity stirred the young belt, raising collision speeds until bodies shattered instead of merging. Most of the original material was flung away; what remains totals only a few percent of the Moon's mass, and Ceres holds a quarter of it.

Not a crowded field

Films show tumbling rock walls, but the real belt is mostly empty space. Pioneer 10 crossed it first in 1972, and every outer-planet mission since has flown through without needing to dodge.

Meteorites

Collisions in the belt knock off fragments that resonances with Jupiter steer onto Earth-crossing orbits. Most meteorites in museum collections began here; the HED meteorites have been traced to Vesta.

Missions

  1. 1972–2003

    Pioneer 10

    NASACompleted

    First spacecraft to cross the asteroid belt and fly past Jupiter (1973).

  2. 2007–2018

    Dawn

    NASACompleted

    Orbited Vesta (2011–2012) then Ceres (2015–2018) with ion propulsion.

  3. 2023–

    Psyche

    NASAEn route

    Mars gravity assist 15 May 2026; arrives at asteroid Psyche Aug 2029.

    Mission page (opens in a new tab)

First-hand · our 3D model

How we render it

In the 3D model the belt is heliocentric, as it is in reality: 2,600 points (1,000 on lighter devices) between 2.1 and 3.3 au from the Sun, not a ring around a planet. Semi-major axes skip the Kirkwood gaps at the 3:1, 5:2, 7:3 and 2:1 resonances with Jupiter, inclinations are realistic, and every point moves at its Keplerian speed on the GPU. Brightness depends on distance from the Sun, distance from the camera and phase angle.

It is deliberately sparse and faint. From Mars, which orbits inside the belt, it reads as scattered points hugging the ecliptic; from Jupiter, outside it, as a distant inclined ellipse. That matches the real belt, which is mostly empty space.

See the belt from Mars in 3D How we built the modelInteractive 3D services
  • CeresDwarf planet · largest body in the asteroid belt
  • 4 VestaA layered protoplanet
  • 16 PsycheA metal-rich world NASA is flying to

Sources

  1. NASA Science: Asteroids (opens in a new tab)
  2. NASA Science: Ceres facts (opens in a new tab)
  3. NASA Science: 4 Vesta (opens in a new tab)

Last reviewed against these sources. Built from public NASA, ESA and JPL data; not affiliated with or endorsed by any agency.